Substantial effort and expense have been devoted to the development of multi-function document processors which combine a photocopying capability with various electronic document processing functions, including facsimile transmission and reception, computer printing, and document editing and storage. Light/lens xerography is still the generally preferred technique for conventional photocopying, and laser based raster input and output scanning have gained widespread acceptance for electronic document processing. Accordingly, the basic challenge is to economically and compactly integrate a laser based raster input and/or output scanning subsystem with a xerographic photocopying subsystem. Another challenge is to obtain reliable, high quality performance from the integrated subsystems. As will be appreciated the ultimate aim is to provide a multifunction document processor which not only favorably compares in performance with dedicated, state of the art photocopiers and laser scanners, but which also has distinct cost and size advantages over the equivalent collection of dedicated equipment.
Significant progress has been made toward meeting the foregoing goal. U.S. Pat. No. 4,241,990, which issued Dec. 30, 1980 on an application of Tibor Fisli for a "Multi-Purpose Optical Data Processor", shows that a laser RIS/ROS capability may be built into the Xerox 3100 copier, without materially degrading its light/lens copying performance. Indeed, in accordance with the teachings of that patent, the laser scanning and copying functions are relatively economically integrated by utilizing shared optics for imaging purposes. Unfortunately, however, the holographic laser scanning mechanism proposed by the above patent does not come up to the high standards of optical efficiency, wide scan angle linearity, and scan field flatness that have been established by the symmetrical, double pass, underfilled, rotating polygon laser scanner of U.S. Pat. No. 4,274,703, which issued June 23, 1981 on an application of Tibor Fisli for "High-Efficiency Symmetrical Scanning Optics." Thus, the objective of efficiently combining a state of the art photocopying capability with a state of the art laser scanning capability has not yet been fully realized.